Planar Cosmology

Author’s Note: The planar cosmology for Chaldea is very similar to what Dungeons & Dragons used in the early 80’s, but with some changes. It’s also consistent with how planes are described in the now out-of-print RPG sourcebook by Wizards of the Coast from 1992, Chessboards: Planes of Possibility, by Dave Howell.

The Chaldean universe is composed of many places. There are worlds that look very much like a “typical” fantasy or medieval setting to strange dimensional warps that look like ladders through space. There are planets, stars, and asteroids like in our world but there are also fantastical fairy lands, elemental seas of fire, and strange dimensional rifts of time and space. Notions like “law” and “water” might simply be moral concepts or states of matter in our world but in Chaldea these are actual places that can be traveled too and there are creatures, albeit strange ones, who live there. There is also the space that connects these places.

Planes of Existence

The central concept in understanding Chaldean cosmology is the notion of planes of existence, or simply planes. Planes are very important because one of the ways that an entity can ascend to godhood is to establish control over a plane of existence. Much of the conflict in the universe stems back to gods or similarly-powerful entities warring against each other for control over planes.

To qualify as a plane, a location must meet three criteria:

  1. Significant size, or scope. The plane doesn’t have to be huge, but it can’t be microscopic either. The smallest known planes are at least several hundred miles across. If the plane is more esoteric in nature, where Euclidian distances might not apply, like “the plane of abstract thought”—-in this case the “scope” of the plane should be important related to the esoterica.
  2. Significant importance. The plane has to be important for some reason other than the notion that some deity wishes it were so. Perhaps there are great civilizations that live there, or it’s the home planet of some unique race, or perhaps it’s completely uninhabited but is the sole source of some rare metal or spice - in which case it might not be important at the moment it’s discovered but could become so quickly. Again, the reason could be more esoteric in nature and the reason for its importance may not be obvious to the entities living or traveling there.
  3. Significant borders. The plane must be contained. It should be obvious where the plane starts and ends and it shouldn’t be trivial to leave it or get to it. You can’t own more planes by dividing up existing ones, or at least not easily. In the real world, Earth could be a plane, but not Europe.

Many, many planes in the cosmos are “prime material planes”. The world of Chaldea is a prime material plane, as would be various worlds from fiction if they were using this model. This is the default. Plants and animals can grow and die, water flows downhill, time moves the way you’d expect, and the plane is most likely a planet set in a solar system somewhere. This varies from the traditional D&D viewpoint where all the planets, stars, and galaxies are “the” prime material plane. In the Chaldean universe we break this up a bit.

Author’s Note: I never liked the notion from early D&D that the deities home planes were all force-fed into the “outer planes” like the Abyss and the Happy Hunting Grounds. The alignment planes are a bit funky anyway and I like to play them a bit more esoterically. Breaking down the D&D prime material plane into a vast collection of individual prime material planes opens up the universe for all sorts of options and allows deities to have their own space, if you will. This solves the question of who dominates Hell, a bunch of arch devils or gods like Hades and Hel? Simple. If you’re talking about the alignment planes, the Nine Hells, then let’s riff off Dante’s Inferno and bring out our favorite arch-devils from the AD&D Monster Manuel like Asmodeus and Dispater and put them large and in charge. If you want to talk about the Hel of Norse Mythology under the roots of Yggdrasil, realm of endless and bitter cold, or the Babylonian underworld where Ishtar descended into and got trapped by Ereshkigal who had her infected with 60 diseases - these are other planes entirely. The Chaldean planar cosmology is designed to help us enjoy the differing atmosphere’s of these various myths without having to figure out how to force them all into the same place. And the Abyss? Bring on the demon lords, baby!

The following planes pretty much follow the AD&D canon: positive material plane, negative material plane, the elemental and para-elemental planes, the ethereal plane, and the astral plane
Alignment planes. The alignment planes are like in AD&D except most deities don’t live here.

Deep Space

The Chaldean cosmology allows for all the stuff you’d expect to find in real world space travel: planets, stars, the moon, the sun (just one each), comets, asteroids, etc. Some planets are important enough to be planes, but most aren’t. A comet or asteroid could be a plane!
However, these celestial objects operate totally differently, in a mystical fashion. When looking up at the night sky it takes less imagination to visualize the signs of the zodiac and the other constellations, and their movements through the universe really do influence the natural and mystical order of things.

There is no astronomy, there’s only astrology. It’s one study and it’s advanced practitioners use it to study the influences of celestial activities on terrestrial activities. Casual practitioners use it to aid in ocean navigation and orienteering.


Dimensions and planes are not the same thing. Where planes represent different locations and exhibit the characteristics described earlier, dimensions are more like funny math games that GM’s and players can use to explore violations of Euclidean 3D space, typically without ever leaving the plane they started from. Phenomena like dimension door, teleportation, “being out of phase”, portable holes, and rope tricks involve playing tricks with the special fabric of the plane you happen to be on at the time. And on some planes these effects may not work or may work differently - adventurer beware!

Author’s Note: I recommend you sorta gloss over how this “really” works unless you have advanced degrees in math—-which I don’t. All I really recommend as “canon” is that planes and dimensions be “different” although there could certainly be some hybridization of them. Maybe plane shifting from one planet to another through space is really dimensional travel? If you like this stuff, have fun!

Planar Cosmology

Chaldea PeterAdkison